EHV-1 Outbreak: State Veterinarians Monitoring Closely

The number of horses affected by the neurologic equine herpesvirus-1 (EHV-1) outbreak in the western United States and Canada continues to rise. Since health officials identified the virus as stemming from involvement with the National Cutting Horse Association (NCHA) Western National Championship competition, held April 28-May 8 in Ogden, Utah, the number of confirmed cases has reached the double digits.

Equine herpesvirus is highly contagious and can cause a variety of ailments in horses, including rhinopneumonitis (a respiratory disease mostly of young horses), abortion in broodmares, and myeloencephalopathy (evident in the neurologic form). The virus is not transmissible to humans. Clinical signs of the neurologic EHV-1 form include fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence. The virus is generally passed from horse to horse via aerosol transmission (when affected animals sneeze/cough) and contact with nasal secretions.

State and provincial veterinarians are keeping close tabs on the number of confirmed and suspected EHV-1 cases. Since there is no centralized data reporting system, case counts are based on reports from individual states (although the Veterinary Infection Control Society has been collecting information regarding suspected and confirmed cases).

Utah State Veterinarian, Bruce L. King, DVM, said, "At this point we have had no confirmed cases of EHV-1 in Utah since the NCHA show that was held in Ogden. We do have some suspect horses that were at the show that laboratory confirmation is pending."

California now has 10 confirmed cases of EHV-1, according to a news release from the California Department of Food and Agriculture. A total of 54 horses from California competed at the NCHA championships.

Canada veterinarians also are on the lookout for cases. "Our office has been notified of one case of (neurologic) EHV-1 in the province of Alberta," said Chief Provincial Veterinarian Gerald Hauer, DVM. "The horse has been attended by a veterinarian, is isolated, and is recovering."

Idaho agriculture released a statement indicating that two horses were euthanized that exhibited clinical signs consistent with neurologic EHV-1 and "several others" are under veterinary care, but there have been no confirmed cases.

Washington saw its first EHV-1-positive case discharged from Washington State University's (WSU) Veterinary Teaching Hospital on May 13. Today Debra C. Sellon, DVM, PhD, Dipl. ACVIM, a professor of equine medicine at WSU, reported that since the discharge all PCR diagnostic tests run on hospital patients have been negative, and the university hospital remains under quarantine.

Today (May 18) a second case of EHV-1 was confirmed. The horse presented with neurologic signs and was taken to Pilchuck Veterinary Hospital (PVH) in Snohomish. Attending veterinarian Wendy Mollat, DVM, Dipl. ACVIM, said in a press release issued by the hospital that upon presentation to PVH, "the horse was immediately admitted to our designated equine isolation facility and has not been allowed direct or indirect contact with our general equine population. The horse is clinically stable and will remain hospitalized until confirmed to be no longer shedding the virus."

Oregon confirmed its first case of EHV-1 today when one horse that attended the NCHA competition produced a positive test. A press release issued by the state Department of Agriculture indicated there are no travel restrictions on non-exposed horses at this time.

New Mexico Livestock Board officials issued a press release from indicating that there are two suspected EHV-1 cases in that state, however both horses are currently under quarantine and veterinary treatment. There were no confirmed cases at press time. Additionally, all New Mexico horses that attended the NCHA show are under voluntary quarantine at their regular barns and are being monitored for signs of disease.

Currently Unaffected States on High Alert

Fortunately, authorities in some Western states have not received reports of any EHV-1 positive horses. Nonetheless, veterinarians and horse owners remain on high alert and are taking precautionary steps to prevent the spread of any possible disease.

"At this time there are no EHV-1 positive or suspect horses in Wyoming that we are aware of," said State Veterinarian Jim Logan, DVM. "We do know that there were some horses that attended the Ogden event and returned to Wyoming. All of these animals have been accounted for, are isolated, and under movement restriction and observation by veterinarians. None have shown any clinical signs to date."

The Texas Animal Health Commission (TAHC) issued a statement yesterday (May 17) indicating that there are no EHV-1 positive horses in the state currently, and the commission "has no plans to change entry requirements for equine animals or to cancel any equine events at the present time."

Both North and South Dakota state veterinarians--Susan J. Keller, DVM, and Dustin Oedekoven, DVM, respectively--said that EHV-1 has not been confirmed in their states. Oedekoven added that none of the horses that attended the Ogden show from South Dakota were showing any clinical signs of the disease.

Likewise, State Veterinarian Phil LaRussa, DVM, said Nevada is free of EHV-1 at present.

Shifting Transportation Requirements

The Colorado Department of Agriculture issued a press release yesterday, introducing new travel requirements for any horses entering the state.

Horse owners must obtain a permit to enter the state in addition to presenting the standard health certificate (issued within 30 days prior to entry) and a proof of a current negative Coggins test.

"Horse owners who wish to bring their horse into Colorado must first call their veterinarian," the department press release stated. "That veterinarian can then contact the Colorado Department of Agriculture's State Veterinarian's Office at 303/239-4161 and request a permit number. That number would then be included on the health certificate."

"We are considering all of our options for protecting Colorado's horse industry," State Veterinarian Keith Roehr, DVM, said in the press release. "At this point, we do not believe it's necessary to stop horses from entering the state but we need to be able to know where those horses are coming from and where they are going; trace-back is a vital part of disease control."

Yesterday the NCHA released a statement on its website indicating that while the organization was not requiring show producers to cancel or reschedule shows, it urged these individuals to make horse health the No. 1 priority: "While the NCHA is at present not mandating cancellation of all shows nationwide, we do strongly urge all show producer(s) to consider the possible horse health risks of conducting an event until the extent of the virus can be determined and contained."

Additionally, the American Paint Horse Association released a list of shows canceled due to the EHV-1 outbreak on the organization's website.

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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